Here are the biggest things to watch for during James Comey's blockbuster hearing

James Comey, the ousted FBI director, testifies before the Senate
Intelligence Committee on Thursday in what is certain to be one
of the most-watched political events in recent history.

Comey preempted his hearing by authorizing the
release of his opening remarks for testimony on Wednesday,
giving reporters and political observers time to comb through
what the former FBI director plans to say about his private
communications with President Donald Trump.

Before Trump fired him in early May, Comey oversaw the FBI's
investigation into whether the Trump campaign colluded with
Russian officials to interfere in last year's presidential
election.

Now that we know what Comey plans to say before the committee in
his opening remarks, here's what to watch for.

Comey was careful in his written testimony not to make any
assertions about whether the president obstructed justice or
attempted to obstruct justice in his conversations with the FBI
director, outlining what he said the facts of those conversations
were. But leading senators on the panel are likely to ask Comey
about whether he believes Trump's actions constitute obstruction
of justice, the same charge that
eventually led President Richard Nixon to resign during the
Watergate scandal.

2. Will Comey confirm Trump's account that the FBI director
assured the president on three occasions that he was not under
investigation?

In his written testimony, Comey said he told Trump on three
occasions that he was not the subject of a counterintelligence
investigation. But according to Comey's written testimony, Trump
became upset that Comey would not confirm so publicly, which
Comey said could create a problem if that status were to change.

Senate Intelligence Committee members are likely to ask Comey
about those instances. If Comey says the president was correct in
that characterization, Trump's supporters both on Capitol Hill
and elsewhere will zero in on that as evidence that Trump was in
the right.

3. Why didn't Comey take this information to top Justice
Department officials?

Some have questioned why Comey did not tell his superiors about
his concerns about his conversations with Trump. Comey gave
details to senior FBI officials, but he apparently did not tell
top Justice Department leaders, such as Attorney General Jeff
Sessions, the nitty gritty about what had unnerved him in those
conversations. If Comey believed Trump's actions were extremely
concerning, senators will ask why he didn't raise those concerns
with the top officials in his department.

4. How much does he expand on his testimony?

Comey's written testimony confirms the news accounts that
revealed these bombshell claims in the immediate aftermath of his
firing, but it did not provide much additional information that
had not already crept into the public realm. While Comey will
most likely be grilled for hours, how much will he expand on, and
how much new information will he provide?